WASHINGTON — The Bush administration is going ahead with a controversial pilot program giving Mexican trucks greater access to U.S. highways, despite a new law by Congress against it.

The decision to proceed with the four-month-old program, which allows participating Mexican trucking companies to send loads throughout the United States, comes despite language in the recently signed catchall spending bill aimed at blocking it.

But the Department of Transportation is taking advantage of a loophole in the new law, which prohibits the government from spending any money to “establish” the program. The government says the new rules don’t apply to the current program since it started in September.

“The U.S. Department of Transportation will not establish any new demonstration programs with Mexico,” said Federal Motor Carrier Safety Administration spokeswoman Melissa Mazzella DeLaney. “The current cross-border trucking demonstration project — established in September — will continue to operate in a manner that puts safety first.”

Congressional opponents of the programs insist that it’s clear what lawmakers were trying to do last year when both the House and Senate voted against allowing the program to go forward.

The provision, as signed by President Bush last month, says: “None of the funds made available under this act may be used to establish a cross-border motor carrier demonstration program to allow Mexico-domiciled motor carriers to operate beyond the commercial zones along the international border between the United States and Mexico.”

“They know what the law says,” retorted Sen. Byron Dorgan, D-N.D., who won a 74-24 vote to block the program. “And they’re not above the law.” Dorgan warned they better follow the law.

The hotly contested program, opposed by labor, independent truck owners and environmental groups, permits up to 500 trucks from 100 Mexican motor carriers full access to U.S. roads.

Opponents have been fighting the measure — part of the 1994 North American Free Trade Agreement — since it was first proposed, saying the program will erode highway safety and eliminate U.S. jobs. And they say that insufficient safeguards exist to make sure that Mexican trucks are as safe as U.S. carriers.

Supporters of the plan say letting more Mexican trucks on U.S. highways will save American consumers hundreds of millions of dollars. And they say U.S. trucking companies will benefit since reciprocal changes in Mexico’s rules permit U.S. trucks new access to that country.

Since 1982, Mexican trucks have had to stop within a buffer border zone and transfer their loads to U.S. trucks.

Still, there’s widespread opposition to the program within Congress. The House voted without a roll call in July to block the program and the Senate’s 3-to-1 margin in September to block it came despite administration assurances that safeguards are in place to “ensure a safe and secure program.”

The Teamsters Union, Sierra Club and Public Citizen joined together in a lawsuit filed in August seeking to block the program.

A hearing is scheduled for Feb. 12 before the 9th Circuit Court of Appeals in San Francisco, Teamsters spokeswoman Leslie Miller said.